When lighting large areas, such as athletic fields, baseball diamonds, football fields and the like, it is important that the light intensity be closely controlled. Experience has indicated that different sports require a different degree of illumination, and in some instances, baseball for instance, the degree of illumination required in the outfield may be different than that necessary to light the infield.
When illuminating sports fields it is important that the light intensity be substantially uniform over the primary playing area wherein "light" or "dark" localized conditions be avoided. Significant localized differences in the degree of illumination of an athletic field make it very difficult to observe and accurately locate and track a moving object, i.e. a ball in flight, and control and uniformity of illumination is very important.
As the intensity of illumination is related to the distance of the portion of the field being illuminated from the luminaire the distance of the luminaire from the field portion being lighted is a significant factor, but as the operating costs of illuminating an athletic field is significant it is important that the lighting system be as economical to operate as possible, and of course, the cost of original installation of the system is of significance.
Areas being illuminated are often located in residential or relatively high population density areas, and the lighting of an athletic field is often objected to by nearby residents due to the light pollution occurring resulting from light "spillage."
It is known to endeavor to uniformly illuminate athletic fields by the use of luminaire reflectors, shields, lenses, screens and the like wherein attempts are made to focus the light in a desired direction. Prior art systems have not successfully provided efficient uniform illumination over relatively large areas with a minimum of light spillage, and often, where a high degree of illumination is required, the lighting systems are "over-designed" producing "hot spots" and sacrificing efficiency of operation. Further, many lighting systems for athletic fields are not capable of adequately confining the projected light resulting in the creation of light pollution and ill feelings by neighbors due to light spillage.
It is an object of the invention to provide an outdoor lighting system utilizing parabolic reflectors wherein highly efficient uniform lighting of an area may be achieved with a minimum of apparatus, i.e. lighting fixtures, and wherein the apparatus may be relatively economically produced.
Another object of the invention is to provide an outdoor lighting system employing parabolic reflectors wherein the reflecting surface includes a plurality of small light directing surfaces of an elliptical configuration to direct and evenly distribute reflected light.
A further object of the invention is to provide an outdoor lighting system utilizing a parabolic reflector having a plurality of reflecting surfaces defined thereon for substantially evenly distributing the reflected light over an area even though the light is obliquely directed upon the area.
Yet another object of the invention is to provide an outdoor lighting system utilizing a parabolic reflector wherein light reflected in an oblique direction over the area to be lighted is substantially evenly distributed over such area without the use of lenses and shields.
In the practice of the invention the lighting system utilizes a substantially parabolic reflector in conjunction with a high intensity lamp, such as of the metal halide type, the lamp light source being located at the focal point of the reflector. Usually, the reflector is formed of metal having a highly light reflective inner parabolic surface. In planes perpendicular to the reflector axis the reflector is circular in configuration and includes upper, lateral and lower regions.
A basic concept of the invention involves the use of oval or elliptical peen configurations to modify a circular beam of light into an oval beam. Such a modified light beam is particularly suitable for distributing light over areas located at an intermediate distance from the light source, i.e. the central regions of a football field lighted by luminaires located at the sides of the field. The peening produces a plurality of adjacent elliptical depressions and ridges which are relatively parallel having their major length substantially vertically oriented and the light being reflected due to the peening of the reflective surface is transmitted in an oval beam having its major dimension identically oriented to the major dimension of the peened configurations.
In one embodiment of the invention the peenings may extend throughout the entire area of the light reflecting surface, but in other embodiments of the invention the peening may only occur over a portion of the reflector surface and other configurations in the reflecting surface are utilized to shape the light beam in the most efficient manner.
In such other modifications a portion of the reflecting surface, such as the lower region, may be peened with a plurality of oval peen marks having a primary dimension substantially vertically oriented while the lateral and upper regions of the reflector may be provided with a plurality of concentric radial flutes or steps. At the reflector lateral regions the flutes may contain elliptical reflecting depressions wherein the dimension of the major axis of the depression is only slightly greater than the minor axis dimensions, and at the flutes located at the reflector upper region, the flutes may be smooth surfaced to minimize light diffusion and produce maximum light reflection for lighting the areas the greatest distance from the reflector. Such a reflector having three types of light directing and controlling surfaces is capable of evenly distributing the light over areas at different distances from the reflector.